1. Field of the Invention
The present invention relates generally to a distributor and more particularly to a rotor brush of distributor treated to suppress electromagnetic noise waves, hereinafter referred to simply as noise waves, generated by the distributor.
2. Description of the Prior Art
It is well known that a distributor provided in a vehicle, such as an automobile or the like, generates noise waves by spark discharges intermittently generated at high rates which interfere with radio and television broadcasting, various kind of radio communication, etc.
These noise waves are becoming an increasingly serious problem because of the recent tendency towards the generation of a strong spark discharge in an ignition device by a large current in a short time in order to purify the exhaust gases.
Hitherto, various proposals have been made for suppressing these noise waves, but exceedingly few of them have been put into practical use because of their high cost in the mass production of vehicles or because of their poor performance. Typical of the noise suppressing means which have been put into practical use is one in which the surface of at least one of the discharge electrodes respectively provided on the rotor brush and a side terminal, which are facing each other to form a discharge gap in the distributor, is additionally provided with a coating of highly resistive material, as mentioned in the specification of Japanese Patent Application No. Sho 49-072663, corresponding to U.S. patent application Ser. No. 566,935, filed Apr. 10, 1975. Now U.S. Pat. No. 4,007,342 issued Feb. 8, 1977. For example, a rotor brush is composed of a silicon wafer, the surface of which is formed with a coating of highly resistive material or a silicon oxide coating by the silicon wafer per se. Alternatively, the rotor brush and side terminal are each composed of a brass material or a resistive alloy invar or the like and the surface of each of the respective discharge electrodes of the rotor brush and the side terminal is deposited, by a spraying method, with a resistive material, such as copper oxide, aluminum oxide, resistive alloy invar or the like.
In the examples described herein, silicon is the most superior material in providing nose wave suppressing characteristics. However, silicon has certain disadvantages in that it is very expensive for the mass production of vehicles and it requires after-treatment to form a coating of silicon oxide as a highly resistive material. While a rotor brush, upon which copper oxide or the like is spray-deposited, is economically practical, there are other disadvantages in such cases in that such a sprayed rotor brush is inferior to the silicon wafer rotor brush as to the noise wave suppressing effect attained, in that the surface of such a sprayed rotor requires shot-blast treatment and further requires a deposition by spraying of nickel aluminide or the like as a foundation, in order to increase the stickiness thereof prior to the treatment of spraying copper oxide or the like, and in that the discharging gap has to be specially designed taking into consideration the thickness of the sprayed material, which comes to several millimeters.